1. Field of the Invention
The present invention relates to a structure of a steering support beam for a vehicle and more particularly to a steering support beam having a double walled structure.
2. Prior Arts
In a motor vehicle, as an example of the conventional arts, a steering shaft is mounted on a steering support beam which is transversely provided on a front deck between left and right front pillars. Generally, the steering support beam is composed of a single walled pipe whose both ends are connected with the left and right front pillars, respectively and is supported at the middle portion thereof by supporting stays extended from the lower portion of the front deck. The steering shaft is mounted on the middle portion of the steering support beam through a bracket.
As another example of relating prior arts, Japanese Utility Model Application Laid-open No. Jitsu-Kai-Shou 62-127861 proposes a structure of the steering support beam, in which a pipe is connected at an end thereof with a front pillar. Further, the pipe is connected at the other end thereof with a pipe-shaped member split into two pieces such that the pipe overlaps the pipe-shaped member. Further, the member is connected at the other end thereof with a front pillar on an opposite side. The overlapped length of one piece of the member differs from that of the other piece thereof.
The steering support beam according to the former example has a problem that since it is constituted by a singe walled pipe, the steering support beam tends to cause a deformation such as a warp and the like due to the heat effect when the stays or the bracket are welded on the beam and as a result this makes it difficult to secure dimensional tolerances. Further, due to the mechanical weakness coming from the structure of the single walled pipe, it is required to increase the diameter of the pipe.
Further, the steering support beam according to the latter example has a different overlapped length between two pieces of the pipe-shaped member and this structure prevents the beam from being broken at a portion having a large change in the cross-sectional area, when an impact is applied to the beam from outside. However, since the steering support beam is also constituted by a single walled pipe, it is difficult to secure an adequate rigidity and strength.
Further, the steering support beam has a difficulty in connecting the pipe with the pipe-shaped member by welding and this is not desirable from the point of view of productivity.